How to add the source of Ubuntu Tweak

open your terminal, first import the key:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com FE85409EEAB40ECCB65740816AF0E1940624A220
type the command to run gedit(or other editor in your opinion) to modify the sources.list:
sudo gedit /etc/apt/sources.list
And put the two line into it(If you are using Ubuntu 8.04 Hardy or early) :
deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu hardy main
deb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu hardy main
Or Ubuntu 8.10 Intrepid:
deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu intrepid main
deb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu intrepid main
Or Ubuntu 9.04 Jaunty:
deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu jaunty main
deb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu jaunty main
Or Ubuntu 9.10 Karmic:
deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu karmic main
deb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu karmic main
Then update the source and install or upgrade Ubuntu Tweak:
sudo apt-get update
sudo apt-get install ubuntu-tweak